CHARACTERISTICS OF RESTITUTION KINETICS IN REPOLARIZATION OF RABBIT ATRIUM

The study was designed to characterize restitution kinetics in atrial repolarization of rabbits and to examine effects of K+ or Ca2+ channel blockers on restitution. Action potentials were recorded from rabbit atrial tissue. Restitution curves of phase 1 amplitude and action pote ntial duration at 50 and 90% repolarization (APD(50), APD(90)) were de fined at a basic cycle length of 0.5 s during control and with interve ntions, Restitution of phase 1 amplitude had a monoexponential functio n with a time constant of 2.8 +/- 0.2 s. The curves of APD(50) frequen tly had a monoexponential function and time constants were 1.8 +/- 0.1 s. Restitution curves of APD(90) were biphasic: a descending phase fo llowed by an ascending phase. The blocker of I-Kr (a 4-aminopyridine-s ensitive component of the transient outward current), 4-aminopyridine, flattened the restitution curves of phase 1 amplitude, and APD(50) an d APD(90) curves became monophasic. Sotalol, a selective I-Kr (a rapid component of the delayed rectifier K+ current) blocker, did not alter curves of phase 1 amplitude and APD(50) but shifted APD(90) curves up ward. Cadmium, a Ca2+ blocker shifted curves ofphase 1 amplitude and A PD(50) downward and abolished the ascending phase of APD(90) curves. W e conclude that kinetics of I-tol and I-ca (calcium current) may accou nt for characteristics of restitution of atrial repolarization in rabb it.